Giant panda fans got two tiny pieces of good news Saturday as the Smithsonian’s National Zoo in Washington announced the births of a pair of new panda cubs.

The zoo announced the surprising second delivery by mother Mei Xiang late Saturday, about five hours after kicking off regionwide excitement with news of the first cub.

The sexes of each newborn will be determined at a later date.

In a lengthy statement following the first birth, the zoo said Mei Xiang reacted favorably to the cub by picking it up.

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“All of us are thrilled,” said zoo director Dennis Kelly. “The cub is vulnerable at this tiny size (of about 4 centimeters), but we know Mei is an excellent mother."

The zoo said veterinarians first detected evidence of a fetus on August 19, about one month after Mei Xiang began exhibiting signs of pregnancy or pseudopregnancy.

Signs of pregnancy

Those signs included nest building, spending more time in her den, sleeping more and eating less. The mother also spent more time licking and cradling toys.

Veterinarians expect Mei Xiang to spend almost all of her time in seclusion with her cubs for the next two weeks. The giant panda habitat has been closed to the public until further notice to provide them some quiet.

Veterinarians artificially inseminated Mei Xiang with semen collected from a giant panda who lives at a research center in central China. Officials said donor Hui Hui was found to be the best genetic match for Mei Xiang.

Before Saturday, Mei Xiang had given birth to two surviving cubs, Tai Shan and Bao Bao. Tai Shan was born in 2005 and now lives in China.

Bao Bao, born two years ago Sunday, still lives at the zoo and will remain there until age 4. She will then return to China and eventually enter China’s giant panda breeding program.

Both Tai Shan and Bao Bao were born as the result of artificial insemination.